Map Reduce输出文件为空

Question

我正在Hadoop中编写一个程序，以便在不同年龄组中按性别查找薪水最高的员工，该员工成功运行，但输出文件为空。有关详细信息，请参阅http://www.tutorialspoint.com/map_reduce/map_reduce_quick_guide.htm

计划

public class PartitionerExample extends Configured implements Tool
{
   //Map class

   public static class MapClass extends Mapper<LongWritable,Text,Text,Text>
   {
      public void map(LongWritable key, Text value, Context context)
      {
         try{
            String[] str = value.toString().split("\t", -3);
            String gender=str[3];
            context.write(new Text(gender), new Text(value));
         }
         catch(Exception e)
         {
            System.out.println(e.getMessage());
         }
      }
   }

   //Reducer class

   public static class ReduceClass extends Reducer<Text,Text,Text,IntWritable>
   {
      public int max = -1;
      public void reduce(Text key, Iterable <Text> values, Context context) throws IOException, InterruptedException
      {
         max = -1;

         for (Text val : values)
         {
            String [] str = val.toString().split("\t", -3);
            if(Integer.parseInt(str[4])>max)
            max=Integer.parseInt(str[4]);
         }

         context.write(new Text(key), new IntWritable(max));
      }
   }

   //Partitioner class

   public static class CaderPartitioner extends
   Partitioner < Text, Text >
   {
      @Override
      public int getPartition(Text key, Text value, int numReduceTasks)
      {
         String[] str = value.toString().split("\t");
         int age = Integer.parseInt(str[2]);

         if(numReduceTasks == 0)
         {
            return 0;
         }

         if(age<=20)
         {
            return 0;
         }
         else if(age>20 && age<=30)
         {
            return 1 % numReduceTasks;
         }
         else
         {
            return 2 % numReduceTasks;
         }
      }
   }

   @Override
   public int run(String[] arg) throws Exception
   {
      Configuration conf = getConf();

      Job job = new Job(conf, "topsal");
      job.setJarByClass(PartitionerExample.class);

      FileInputFormat.setInputPaths(job, new Path(arg[0]));
      FileOutputFormat.setOutputPath(job,new Path(arg[1]));

      job.setMapperClass(MapClass.class);

      job.setMapOutputKeyClass(Text.class);
      job.setMapOutputValueClass(Text.class);

      //set partitioner statement

      job.setPartitionerClass(CaderPartitioner.class);
      job.setReducerClass(ReduceClass.class);
      job.setNumReduceTasks(3);
      job.setInputFormatClass(TextInputFormat.class);

      job.setOutputFormatClass(TextOutputFormat.class);
      job.setOutputKeyClass(Text.class);
      job.setOutputValueClass(Text.class);

      System.exit(job.waitForCompletion(true)? 0 : 1);
      return 0;
   }

   public static void main(String ar[]) throws Exception
   {
      int res = ToolRunner.run(new Configuration(), new PartitionerExample(),ar);
      System.exit(0);
   }
}

程序运行成功，但输出文件未显示任何输出。这是我的输出：

Answer 1

也许#include <iostream> #include <stdexcept> class derived_exception : public std::exception { public: derived_exception(const std::exception& exception) { } }; int main(int argc, char** argv) { try { throw std::exception("test"); } catch (const derived_exception& exception) { std::cout << exception.what(); } return 0; } 应为job.setOutputValueClass(Text.class);

reducer签名是job.setOutputValueClass(IntWritable.class);。

Answer 2

您的reduce方法不会覆盖基类的reduce方法。可能添加@Override注释可以解决此问题。